1. Field of the Invention
This invention relates to methods for controlling an apparatus using a two-channel safe regulation arrangement.
2. Description of the Prior Art
In known arrangements for safely regulating an apparatus, a nominal or desired value is converted into an input variable in two channels parallel to each other and is supplied to the apparatus, such as a mechanical apparatus. An output variable of the apparatus is picked up and, after feedback, is compared with the nominal value. In this manner, the apparatus is controlled or regulated into a safe state of operation when different input variables occur at the output of the two channels.
In order to obtain a secure regulation, two regulation circuits are thus superposed. Each regulator has its own channel and its own sensor that detects the apparatus output variable. In order to check the results of the two regulation circuits, a so-called fail-safe comparator is included. This fail-safe comparator generates a shutdown signal that controls or regulates the apparatus into a safe state of operation when the regulation signals on the apparatus do not coincide. Such a two-channel structure is known from the book entitled "Mikrocomputer in der Sicherheitstechnik" (Microcomputers in the safety technology) by H. Holscher and J. Rader, Verlag TUV-Rheinland 1984, Chapter 7.3.
The use of two sensors in such a safety regulation arrangement is often undesirable since the sensors can be expensive, depending on the apparatus output variable to be measured.
It is an object of the present invention to provide two-channel safety regulation of apparatus that works with only one sensor with at least the same security as the prior art arrangements.